Engine control method and apparatus

ABSTRACT

An improved method and system for the control of an engine system such as the spark timing. The control senses the speed variations either during a portion of a complete cycle and a complete cycle and/or from cycle to cycle in order to determine the load on the engine from preprogrammed maps based upon the engine characteristics. From this load and the speed reading, it is possible to obtain the desired engine control. This not only reduces the costs of the system by reducing the number of sensors, but also permits adjustments to be made more rapidly.

BACKGROUND OF INVENTION

This invention relates to an engine control method and apparatus and more particularly to an improved, simplified, highly effective and yet low cost arrangement for such control.

In internal combustion engines, a wide variety of systems and methodology are employed for engine control. Generally, smaller and lower volume engine applications incorporate generally less sophisticated controls than those employed on larger production volume engines such as automotive engines. Even in the small displacement lower production volume engines, for example those used in motorcycles, the engine control can become quite complicated.

For example and as shown in FIG. 1 the spark control for a motorcycle engine is shown schematically. The control arrangement is intended to control the firing of a spark plug 21 associated with an internal combustion engine 22 that powers the motorcycle, which is not shown in this figure, but which may be of a construction as generally shown in FIG. 3. An amplified spark voltage is applied to the spark plug 21 from an ignition coil 23, which, in turn, is controlled by an ignition timing control arrangement, indicated schematically at 24. This timing control arrangement 24 receives the inputs from a number of engine-associated sensors. These include a crankcase rotational speed sensor 25 which may comprise a pulser coil and a throttle position sensor 26, which is coupled to the throttle control mechanism for the engine 22 and inputs a signal to the control 24 indicative of engine load and/or operator demand.

Electrical power is provided to the ignition control circuit 24 from a battery 27 through a main switch 28. This battery power is applied to a power source circuit 29 of the control 24 and specifically to an electronic circuit 31 which may comprise a microprocessor.

The output from the engine speed sensor 25 is transmitted to a rotational speed detector circuit 32, which counts the number of pulses generated in a time period so as to determine the rotational speed of the crankshaft of the engine 22.

This outputs a speed signal N to an ignition timing determining circuit, indicated at 33. In addition, the throttle position sensor 26 inputs a signal to a throttle position detector circuit 34. This detector circuit 34 outputs a signal a to a throttle opening calculating circuit 35. This, in turn, outputs a throttle angle position θ to the ignition timing determination circuit 33.

From these inputs, the ignition timing determining circuit outputs a signal at a time determined from maps contained in a memory of the circuit 31 to an ignition circuit 36 which may be of the capacitor discharge type so as to output an electrical output “i” to the coil 23 which is stepped up by the coil 23 to a value “l” for firing the spark plug 21 in a well-known manner.

FIG. 2 is a graph showing one of the maps which may be incorporated in the circuit 31 and shows how the spark timing is varied in response to engine speed for given load as determined by the throttle opening circuit. There may be a family of such curves so as to vary the ignition timing in response to both throttle position and engine speed.

Rather than using a throttle position sensor, load may be sensed by intake manifold vacuum. Either method, however, requires added sensors, transducers and circuitry.

It has been found that merely using engine speed and load as detected by something such as a throttle position or intake manifold vacuum sensor does not actually provide as good a control as desired. That is, these two factors by themselves may not be sufficient to provide the desired degree of control.

Although systems have been provided for automotive applications wherein more sophisticated controls are employed, this further adds to the cost of the system and does not always provide the optimum results.

There have also been other devices than throttle position sensors or vacuum sensors for sensing intake manifold vacuum for determining engine load. It also has been determined that engine load may be found by comparing engine speed from one revolution to another.

However, these systems also tend to be complicated and do not lend themselves particularly low production volume, low cost vehicle applications. They also have the disadvantage of requiring a plurality of different types of sensors.

Other arrangements have been proposed wherein engine speed is measured for less than one complete revolution of the engine and variations from cycle to cycle have been employed to determine engine load. These systems, however, have for the most part, required multiple sensors and also require some delay from the sensed conditions before adjustment is being made.

It is, therefore, a principal object to this invention to provide an improved engine control system wherein the number of sensors employed for achieving optimum engine control is substantially reduced.

It is a further object to this invention to provide an arrangement for controlling an engine system utilizing only a single sensor and a single timing mark associated with a driven engine shaft so as to substantially reduce the costs, without significantly decreasing the efficiency or the obtaining of an optimum control.

Also, it should be understood although a specific example of engine ignition timing control is disclosed and has been described, other engine systems also may be controlled in a like manner such as fuel control with either fuel injection or other forms of fuel supply and throttle control for fly-by wire throttle systems. Other engine control applications with which the invention may be employed will present themselves to those skilled in art from the following description.

SUMMARY OF INVENTION

A first feature of this invention is adapted to be embodied in an internal combustion engine control system and a method for operating an engine by controlling a system of the engine. The engine has a driven shaft and a sensor arrangement is associated with the driven shaft for sensing the instantaneous rotational speed of the driven shaft during the rotation of the driven shaft for less than a complete rotation and for sensing the rotational speed of the driven shaft for a complete revolution that includes the measured less than complete rotation. In accordance with the method and apparatus, the engine system is controlled from these measurements.

Another feature of the invention is adapted to be embodied in a four-cycle internal combustion engine control system for controlling the system of the engine. In accordance with the method and apparatus, the engine has a driven shaft and a sensor arrangement is associated with the driven shaft for sensing the rotational speed of the driven shaft. The rotational speed of the driven shaft during a revolution containing a compression stroke and during a revolution containing an exhaust stroke are made. The engine is controlled from these measurements.

Another feature of the invention is adapted to be embodied in a method and apparatus for an internal combustion engine control system for controlling a system of the engine. The engine has a driven shaft and sensor is associated with the driven shaft for sensing two rotational conditions of the driven shaft during a first rotation thereof. The same two rotational conditions are sensed during the immediately succeeding rotation of the driven shaft and the engine system is controlled on the third rotation of the driven shaft from these measurements.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a partially schematic view showing a prior art type of engine control system.

FIG. 2 is a graphical view showing one of the speed and timing maps for a given engine load utilized in the prior art control system.

FIG. 3 is a side elevational view of the type vehicle which the prior art system can be utilized and also which can utilize the invention.

FIG. 4 is a schematic view, in part similar to FIG. 1 but shows the construction in accordance with an embodiment of the invention.

FIG. 5 is a view showing the timing sensor associated with the engine shaft for the control system.

FIG. 6 is a schematic view showing the method of practicing the invention.

FIG. 7 is a block diagram showing a control routine, which may be utilized to practice the invention.

FIG. 8 is an enlarged view of the load determination portion of the diagram of FIG. 6.

FIG. 9 is a graphical view showing the three-dimensional map utilized to determine the engine timing with respect to engine load and engine speed in FIG. 6.

FIG. 10 is a graphical view showing how the shaft speed varies during the compression stroke with engine speed and load.

FIG. 11 shows the same condition but on the exhaust stroke.

FIG. 12 is a graphical view showing the difference between the speed variations on the compression and exhaust strokes.

FIG. 13 is a graphical view showing how the fuel consumption is improved with this method from the conventional prior art method.

DETAILED DESCRIPTION

Referring now in detail to the drawings and initially to FIG. 3, a motorcycle constructed and operated in accordance with the invention is identified generally by the reference numeral 51. It is to be understood that this specific application for the invention is only a typical one with which the invention may be utilized. A motorcycle is chosen at the exemplary embodiment because the invention, as should be apparent from the foregoing description, has particular utility in conjunction with relatively small, low production volume engines. However, it should also be apparent that the simplicity of the invention lends itself to use with other applications such as automotive application due to the improvement in fuel economy and performance without significant cost penalties.

The motorcycle 51 is comprised of a frame assembly, indicated generally by the reference numeral 52, that dirigibly supports a front wheel 53 on a front fork 54 that is steered by a handle bar assembly 55 in a well-known manner.

A rear wheel 56 is supported for suspension movement relative to the frame 52 by means that includes a trailing arm assembly 57. An engine, indicated generally by the reference numeral 58, and having a combined crankcase transmission assembly 59 is suitably suspended in the frame 52 and drives the rear wheel 56 through a suitable drive arrangement.

The engine 58 has a carburetor 61 to which fuel is supplied from a fuel tank 62 mounted above the engine 58 on the frame assembly 52. A throttle valve is associated with this carburetor 61 and is operated by a twist grip throttle control 63 mounted on the handle bar 55. With conventional systems, but not necessary with this invention, a throttle position sensor 64 is associated with the throttle valve shaft of this throttle valve.

The engine 58 is provided with one or more spark plugs 65 (FIG. 4) that are fired by the ignition system, which will be described shortly.

The combustion gases are discharged from the engine exhaust port through an exhaust pipe 66 and muffler 67, which has an atmospheric discharge.

The engine 58 in accordance with the illustrated embodiment operates on the four stroke principal, but as will become apparent to those skilled in the art, the invention can also be utilized with two cycle engines.

A seat 68 is positioned on the frame assembly 52 to the rear of the fuel tank 62 for accommodating the rider in a well-known manner.

Referring now primarily to FIGS. 4 and 5, the control system for controlling the engine system, in this case the firing of the spark plug 65 will be described in more detail. The engine 58 has a crankshaft 69 to which a flywheel 71 is affixed for rotation in a known manner. Although the invention is depicted in association with a crankshaft positioned sensor, it may be associated with any other shaft that is driven by the engine in timed relation.

A pulser type sensor 72 is associated with the flywheel 71 and specifically with a timing mark 73 affixed to its outer peripheral surface. The timing mark 73 has a leading edge 74 and a trailing edge 75 which, when passing the sensor 72 will output pulses that can be measured so as to measure the time it takes the timing mark 73 to pass the sensor 72. This constitutes an instantaneous rotational speed for the engine 58 during a portion of a complete rotation.

The timing mark 73 is considerably wider, in accordance with the invention, than those normally used. Such widening is not necessarily required, but can improve the control. For example the width of the mark 73 be equal to 60° of crankshaft rotation. The timing mark is set so that it will first trigger a pulse as the engine begins to approach top dead center (TDC) position and another pulse after the crankshaft is at or near top dead center. The specific angles may vary depending upon the particular application.

Nevertheless, because of the four-stroke operation, these pulses are generated at the end of the compression and exhaust strokes. Prior art methods may have utilized speed measurements at the power stroke, but it has been found that the compression and exhaust stroke are much more accurate in providing an indication of engine load and this constitutes one of the features of the invention.

With a two cycle engine the two measurements per revolution will provide adequate information for engine control on the next revolution.

As seen in FIG. 4, the output from the sensor 72 is delivered to an engine system timing control device 76, which contains an ignition circuit 77 which can be basically a conventional ignition circuit of the CDI type, which outputs a signal, “i” to a coil 78 that outputs a pulse “l” for firing the spark plug 65 in a known manner.

This engine timing control system is powered with electrical power from a battery 79 through a main switch 81.

The output from the sensor 72 is transmitted to a rotational speed detection circuit 82, which outputs a signal N indicative of the rotational speed of the engine during each complete revolution cycle. In addition, the outputs from the leading and trailing edges 74 and 75 of the timing mark 73 registered on the sensor 72 are transmitted to a degree of rotational variation detector circuit 83. This circuit 83 outputs a signal indicative of the speed difference to a load calculation circuit 84.

In the described embodiment, the flywheel 71 may be formed of a magnetic material, and the sensor or coil 72 faces the rotational locus of the timing mark 73. In this case, opposite ends of the timing mark 73 are detected from changes in magnetic resistance in the magnetic path passing through the iron core of the coil 72. Alternatively the timing mark 73 may be formed from permanent magnets fixed on the flywheel 71 at positions a given angle away from each other, and the sensor may be a magnetic sensor such as a Hall element for detecting passage of the permanent magnets. Alternatively, the mark may be a slit, which may be detected optically with an LED and a light receiving element.

The load calculating output circuit operates so as to determine a load factor that is derived from as map shown in FIG. 8. This output is delivered to an ignition timing determination circuit 85 which operates in accordance with the control routine shown in FIGS. 6 and 7 so as to output a signal P to the ignition circuit 77 for firing the spark plug 65 at the appropriate time for the engine speed and engine load.

The circuit portions 82, 83, 84 and 85 are all located within a CPU 86 of the engine control system 76.

Referring now primarily to FIG. 6 and later to FIG. 7, the basic control method used in connection with the invention is to measure revolution to revolution changes in speed “R”. From that difference it is possible to determine engine load. Then by consulting a map of ignition control timing and speed, the appropriate ignition timing can be determined.

FIG. 6 shows schematically how the output from the rotational sensor, in the specific example the coil 72 outputs its signal to the circuit portions 82 and 83 to determine the degree of rotational variation R. A first method to determine the degree of rotational variation R is one in which a ratio of detection time “t” of the projection rotation during a portion of a complete revolution to the period T for a complete rotation including that of the time period t. From these two measurements a ratio is determined and the ratio (t/T)≡R is defined as a degree of rotational variation. This method permits adjustment of the engine control on the very next rotation. This method can be used with both two and four cycle engines.

A second method to determine the degree of rotational variation R is one in which ratios (t/T) determined by the first method are determined for both the compression and the exhaust stroke (ie. two crankshaft rotations). This method is preferably used in four cycle engines. Then the difference between the ratios is defined as a degree of variation. That is, the difference (R_(n−1)−R_(n))=D between a ratio (t_(n−1)/T_(n−1))=R_(n−1) for the compression stroke and a ratio (t_(n)/T_(n))=R_(n) for the exhaust stroke are determined for each compression or exhaust stroke. The difference D is determined as a degree of variation. These methods are shown in the upper right hand box of FIG. 6.

FIG. 10 shows the ratio R_(n−1)=(t_(n−1)/T_(n−1)) for the compression stroke in % at varying torques or loading at 40, 80, 120, 160 200 and 240 Newton meters (N-m). For example, if there is no rotational variation, (60°/360°)=0.167 and thus, the ratio is 16.7%. However, the rotational speed of the crankshaft drops on the compression stroke near Top Dead Center (TDC), so that the ratio R_(n−1) becomes large. As seen in FIG. 10, the ratio R_(n−1) and the rotational variation is larger for a smaller engine speeds N and decreases as N increases. Also as the load or torque increases, the curves shift upwardly because the variation increases.

FIG. 11 shows the ratio R_(n)=(t_(n)/T_(n)) for the exhaust stroke in % where an opposite condition prevails. That is rotational variation is smaller for a smaller engine speeds N and increases as N increases. Also, as the load or torque decreases, the curves shift downwardly because the variation decreases.

FIG. 12 shows the difference D=(R_(n−1)−R_(n)) between the ratio R_(n−1) for the compression stroke and the ratio R_(n) for the exhaust stroke, using FIG. 10 and FIG. 11 . Here, values of the rotational variation for every cycle measured during ten periods are averaged to improve the stability of the data. The degree-of-rotational variation detection circuit 83 repeats the foregoing calculation in synchronization with the crankshaft rotation.

The characteristics shown in FIG. 12 are measured on the engine in advance and stored in a memory of a microcomputer. They are stored, for example, as a three-dimensional conversion map shown in FIG. 8. The load calculation circuit 84 determines load (load Nm on the rear wheel) from the conversion map in FIG. 8, using the degree of rotational variation D determined by the degree-of-rotational variation detection circuit 83, and engine speed N. This determination is shown in the middle right hand box in FIG. 6.

Stored in advance in a memory of the microcomputer 76 is the three dimensional map shown in FIG. 9, depending on the specific engine This map shows the relation between load L, engine speed N and ignition timing α. The ignition timing determination circuit 85 determines ignition timing α (Before Top Dead Center “BTDC” in degrees) from the map in FIG. 9, using load L and engine speed N determined by the load calculation circuit 84. An ignition signal p corresponding to the ignition timing α is sent to the ignition circuit 77. As already noted, the ignition circuit 77 causes the spark plug 65 to generate an ignition spark based on the ignition signal p. This is shown in the lower right hand box of FIG. 6 A preferred operation of this embodiment will be described with reference to FIG. 7. First, if at the Step S1 it is determined that the engine is running in an idling state, as it will immediately after a warm start up, ignition timing α is set to a fixed value α1 at the step S2. T, and ignition control is performed at the step S3. The program then repeats to the step S1.

If the engine 58 is found not to be in an idling state at the step S1, the degree-of-rotational variation detection circuit 83 detects the degree of rotational variation D at the step S4. The microcomputer in the electronic circuit 136 determines whether or not the degree of variation D is within a given range of D_(m) to D_(M) at the step S5. If the variation is out of this range, the ignition timing is set to a fixed value α2 or α3 at either the step S6 or S7.

The values of the fixed degrees of advance at idle is about 10° before top dead center. The values of α₂ and α₃ may be in the range of 20° to 30° before top dead center and are set to avoid errors under small deviations in D to avoid the effects of electrical noise.

If within this range of D_(M)-D_(m), the load calculation circuit 84 determines load L using engine speed N determined by the rotational speed detection circuit 82 at the step S8 and looking up the load L from the conversion map of FIG. 8 at the step S9.

The ignition timing determination circuit 85 then determines ignition timing α at the step S10 using this load L and engine speed N and looking up this value from the conversion map in FIG. 9. The ignition timing determination circuit 85 then sends an ignition signal P corresponding to the read ignition timing α to the ignition circuit 77, causing the ignition plug 65 to be fired.

The effect of this embodiment is shown in FIG. 13. This figure shows the improvement in fuel consumption from that of a conventional ignition system. It will be seen that fuel consumption is improved by 2-12%.

Thus, from the foregoing description should be readily apparent that the described method and structure provides a very simple and low cost yet highly effective system for controlling an engine. Although the invention is described in conjunction with the control of the spark timing, as has been noted, the same principle can be utilized in conjunction with fuel and/or throttle control. Also, the system is capable of being used with either two or four cycle engines. Of course, further changes and modifications may be made without departing from the spirit and scope of the invention, as defined by the appended claims. 

What is claimed is:
 1. An internal combustion engine system control for controlling a system of the engine wherein the engine has a driven shaft, a sensor arrangement associated with said driven shaft for sensing the instantaneous rotational speed of said driven shaft during the rotation of said driven shaft for less than a complete rotation and for sensing the rotational speed of said driven shaft for a complete revolution thereof including the measured less than complete rotation, and controlling said engine system from these measurements.
 2. An internal combustion engine system control as set forth in claim 1 wherein the sensor arrangement comprises a single sensor.
 3. An internal combustion engine system control as set forth in claim 2 wherein the control system operated solely in response to the sensed rotational speed condition without any other sensor inputs.
 4. An internal combustion engine system control as set forth in claim 3 wherein the engine is spark ignited and the engine system controlled comprises at least the spark timing.
 5. An internal combustion engine system control as set forth in claim 1 wherein the sensor arrangement cooperates with only a single timing mark on the driven shaft.
 6. An internal combustion engine system control as set forth in claim 5 wherein the single timing mark has a circumferential extent greater than 5°.
 7. An internal combustion engine system control as set forth in claim 5 wherein the sensor arrangement comprises a single sensor.
 8. An internal combustion engine system control as set forth in claim 7 wherein the control system operated solely in response to the sensed rotational speed condition without any other sensor inputs.
 9. An internal combustion engine system control as set forth in claim 8 wherein the engine is spark ignited and the engine system controlled comprises at least the spark timing.
 10. An internal combustion engine system control as set forth in claim 1 wherein the control measures the time taken for the less than a complete revolution (t) and the time (T) for the complete revolution to determine the ratio t/T and estimates the engine load therefrom.
 11. An internal combustion engine system control as set forth in claim 1 wherein the sensor senses the two rotational speeds of said driven shaft during a first rotation of said driven shaft and for sensing same two rotational speeds of said driven shaft during the immediately succeeding rotation of said driven shaft and controls said engine system on the third rotation of said driven shaft from these measurements.
 12. An internal combustion engine system control as set forth in claim 11 wherein the control measures the time taken for the less than a complete revolution (t) and the time (T) for the complete revolution to determine the ratio t/T during each successive rotation, determines the difference (D) between the two ratios and estimates the engine load therefrom.
 13. An internal combustion engine system control as set forth in claim 12 wherein the engine is spark ignited and the engine system controlled comprises at least the spark timing.
 14. An internal combustion engine system control as set forth in claim 12 wherein the control sets a fixed value for the engine system if the engine speed is less than a predetermined value.
 15. An internal combustion engine system control as set forth in claim 14 wherein the predetermined value of the engine speed is a normal idle speed.
 16. An internal combustion engine system control as set forth in claim 12 wherein the control sets a fixed value for the engine system if the value of D is greater than a predetermined value.
 17. An internal combustion engine system control as set forth in claim 12 wherein the control sets a fixed value for the engine system if the value of D is less than a predetermined value.
 18. An internal combustion engine system control as set forth in claim 17 wherein the control sets a different fixed value for the engine system if the engine speed is greater than a predetermined value.
 19. An internal combustion engine system control as set forth in claim 18 wherein the control sets a still further different fixed value for the engine system if the value of D is less than a predetermined value.
 20. An internal combustion engine system control as set forth in claim 12 wherein the engine system control is determined using a conversion map for determining engine load based on the value of D and rotational speed of the engine shaft and a conversion map for determining engine control based on engine load and rotational speed of said engine shaft.
 21. An internal combustion engine system control as set forth in claim 11 wherein the engine operates on a four cycle principle and one of the speed sensings is done on a compression cycle and the other is done on an exhaust cycle.
 22. An internal combustion engine system control as set forth in claim 21 wherein the engine is spark ignited and the engine system controlled comprises at least the spark timing.
 23. An internal combustion engine system control as set forth in claim 1 wherein the control system operated solely in response to the sensed rotational speed condition without any other sensor inputs.
 24. An internal combustion engine system control as set forth in claim 23 wherein the engine is spark ignited and the engine system controlled comprises at least the spark timing.
 25. An internal combustion engine system control as set forth in claim 1 wherein the engine is spark ignited and the engine system controlled comprises at least the spark timing.
 26. A four cycle internal combustion engine system control for controlling a system of the engine wherein the engine has a driven shaft, a sensor arrangement associated with said driven shaft for sensing the rotational speed of said driven shaft, said control measuring the rotational speed of said driven shaft during a revolution containing a compression stroke and measuring the rotational speed of said driven shaft during a revolution containing an exhaust stroke and controlling said engine system from these measurements.
 27. An internal combustion engine system control as set forth in claim 26 wherein the control system operated solely in response to the sensed rotational speed conditions without any other sensor inputs.
 28. An internal combustion engine system control as set forth in claim 26 wherein the sensor arrangement comprises a single sensor.
 29. An internal combustion engine system control as set forth in claim 26 wherein the control measures the time taken for the less than a complete revolution (t) and the time (T) for the complete revolution to determine the ratio t/T during each of two successive rotations the engine load therefrom.
 30. An internal combustion engine system control as set forth in claim 29 wherein the engine system control is determined using a conversion map for determining engine load based on the value of the difference between the two measured ratios and rotational speed of the engine shaft and a conversion map for determining engine control based on engine load and rotational speed of said engine shaft.
 31. An internal combustion engine system control as set forth in claim 30 wherein the engine is spark ignited and the engine system controlled comprises at least the spark timing.
 32. An internal combustion engine system control as set forth in claim 26 wherein the engine is spark ignited and the engine system controlled comprises at least the spark timing.
 33. An internal combustion engine system control for controlling a system of the engine wherein the engine has a driven shaft, a sensor arrangement associated with said driven shaft for sensing two rotational conditions of said driven shaft during a first rotation of said driven shaft and for sensing same two rotational conditions of said driven shaft during the immediately succeeding rotation of said driven shaft and controlling said engine system on the third rotation of said driven shaft from these measurements.
 34. An internal combustion engine system control as set forth in claim 33 wherein the engine is spark ignited and the engine system controlled comprises at least the spark timing.
 35. An internal combustion engine system control method for controlling a system of the engine wherein the engine has a driven shaft, a sensor arrangement associated with said driven shaft for sensing rotational speed of said driven shaft, said method comprising the steps of sensing the rotational speed during the rotation of said driven shaft for less than a complete rotation and sensing the rotational speed of said driven shaft for a complete revolution thereof including the measured less than complete rotation, and controlling said engine system from these measurements.
 36. An internal combustion engine system control method as set forth in claim 35 wherein the sensor arrangement comprises a single sensor.
 37. An internal combustion engine system control method as set forth in claim 36 wherein the control method is done solely in response to the sensed rotational speed condition without any other sensor inputs.
 38. An internal combustion engine system control method as set forth in claim 37 wherein the engine is spark ignited and the engine system controlled comprises at least the spark timing.
 39. An internal combustion engine system control method as set forth in claim 35 wherein the sensor arrangement cooperates with only a single timing mark on the driven shaft.
 40. An internal combustion engine system control method as set forth in claim 39 wherein the single timing mark has a circumferential extent greater than 5°.
 41. An internal combustion engine system control method as set forth in claim 40 wherein the sensor arrangement comprises a single sensor.
 42. An internal combustion engine system control method as set forth in claim 41 wherein the control method is done solely in response to the sensed rotational speed condition without any other sensor inputs.
 43. An internal combustion engine system control method as set forth in claim 42 wherein the engine is spark ignited and the engine system controlled comprises at least the spark timing.
 44. An internal combustion engine system control method as set forth in claim 35 wherein the control measures the time taken for the less than a complete revolution (t) and the time (T) for the complete revolution to determine the ratio t/T and estimates the engine load therefrom.
 45. An internal combustion engine system control method as set forth in claim 44 wherein the engine is spark ignited and the engine system controlled comprises at least the spark timing.
 46. An internal combustion engine system control method as set forth in claim 35 wherein two rotational speeds of the driven shaft are measured during a first rotation of said driven shaft and the same two rotational speeds of the driven shaft are measured during the immediately succeeding rotation of the driven shaft and the engine system is controlled on the third rotation of said driven shaft from these measurements.
 47. An internal combustion engine system control method as set forth in claim 46 wherein the time taken for the less than a complete revolution (t) is measured and the time (T) for the complete revolution is measured to determine the ratio t/T during each successive rotation, determines the difference (D) between the two ratios and estimates the engine load therefrom.
 48. An internal combustion engine system control method as set forth in claim 47 wherein the engine is spark ignited and the engine system controlled comprises at least the spark timing.
 49. An internal combustion engine system control method as set forth in claim 47 wherein a fixed value for the engine system is set if the engine speed is less than a predetermined value.
 50. An internal combustion engine system control method as set forth in claim 49 wherein the predetermined value of the engine speed is a normal idle speed.
 51. An internal combustion engine system control method as set forth in claim 47 wherein a fixed value for the engine system is set if the value of D is greater than a predetermined value.
 52. An internal combustion engine system control method as set forth in claim 47 wherein a fixed value for the engine system is set if the value of D is less than a predetermined value.
 53. An internal combustion engine system control method as set forth in claim 52 wherein a different fixed value for the engine system is set if the engine speed is greater than a predetermined value.
 54. An internal combustion engine system control method as set forth in claim 53 wherein a still further different fixed value for the engine system is set if the value of D is less than a predetermined value.
 55. An internal combustion engine system control method as set forth in claim 54 wherein the engine is spark ignited and the engine system controlled comprises at least the spark timing.
 56. An internal combustion engine system control method as set forth in claim 47 wherein a first conversion map is used for determining engine load based on the value of D and rotational speed of the engine shaft and a second conversion map is used for determining engine control based on engine load and rotational speed of said engine shaft.
 57. An internal combustion engine system control method as set forth in claim 56 wherein the engine is spark ignited and the engine system controlled comprises at least the spark timing.
 58. An internal combustion engine system control method as set forth in claim 46 wherein the engine operates on a four cycle principle and one of the speed sensings is done on a compression cycle and the other is done on an exhaust cycle.
 59. An internal combustion engine system control method as set forth in claim 35 wherein the method is operated solely in response to the sensed rotational speed condition without any other sensor inputs.
 60. A four cycle internal combustion engine system control method for controlling a system of the engine wherein the engine has a driven shaft, a sensor arrangement associated with said driven shaft for sensing the rotational speed of said driven shaft, said method comprises the steps of measuring the rotational speed of the driven shaft during a revolution containing a compression stroke and measuring the rotational speed of said driven shaft during a revolution containing an exhaust stroke and controlling said engine system from these measurements.
 61. An internal combustion engine system control method as set forth in claim 60 wherein the method is operated solely in response to the sensed rotational speed conditions without any other sensor inputs.
 62. An internal combustion engine system control method as set forth in claim 60 wherein the sensor arrangement comprises a single sensor.
 63. An internal combustion engine system control method as set forth in claim 60 wherein the time taken for the less than a complete revolution (t) is measured and the time (T) for the complete revolution is measured to determine the ratio t/T during each of two successive rotations to determine the engine load therefrom.
 64. An internal combustion engine system control method as set forth in claim 63 wherein the method uses a first conversion map for determining engine load based on the value of the difference between the two measured ratios and rotational speed of the engine shaft and a second conversion map for determining engine control based on engine load and rotational speed of the engine shaft.
 65. An internal combustion engine system control method as set forth in claim 64 wherein the engine is spark ignited and the engine system controlled comprises at least the spark timing.
 66. An internal combustion engine system control method for controlling a system of the engine wherein the engine has a driven shaft, a sensor arrangement associated with said driven shaft, said method comprising sensing two rotational conditions of the driven shaft during a first rotation of the driven shaft and for sensing same two rotational conditions of the driven shaft during the immediately succeeding rotation of said driven shaft and controlling said engine system on the third rotation of the driven shaft from these measurements.
 67. An internal combustion engine system control method as set forth in claim 66 wherein the engine is spark ignited and the engine system controlled comprises at least the spark timing. 